S.M.A.R.T. (Self Monitoring Analysis and Reporting Technology)
Technology designed to alert the user to possible hard disk failures before the disk becomes unusable.
S/MIME (Secure Multipurpose Internet Mail Extensions)
Email encryption standard (Cryptographic Message Standard) using PKI (X.509) certificates for confidentiality (digital envelopes) and integrity (digital signatures). S/MIME provides extensions for standard MIME headers.
S/PDIF (Sony/Phillips Digital Interface)
A high-quality audio port that uses coax cabling with RCA connectors or fiber optic cabling and connectors. S/PDIF supports surround sound speakers.
SATA (Serial ATA)
The most widely used interface for hard disks on desktop and laptop computers. It uses a 7-pin data connector with one device per port. There are three SATA standards specifying bandwidths of
1.5 Gbps, 3 Gbps, and 6 Gbps, respectively.
SATA drives also use a new 15-pin power connector, though adapters for the old style 4-pin Molex connectors are available.
External drives are also supported via the eSATA interface.
SC (Subscriber Connector)
Push/pull connector used with fiber optic cabling.
A text file containing commands or instructions that are performed by a program on the computer rather than by the computer itself.
(Small Computer Systems Interface)
A legacy expansion bus standard allowing for the connection of internal and external devices.
- SCSI 1 defines the original 8-bit bus with a transfer rate of 5 MBps.
- SCSI 2 features a 16-bit data bus implementation (Wide SCSI) and a faster transfer rate (Fast SCSI) while maintaining backward compatibility with most of the original devices.
- SCSI 3 introduces further data rate enhancements (Ultra SCSI) and a serial SCSI standard (Firewire). Each device on a SCSI bus must be allocated a unique ID. The bus must also be terminated at both ends.
SDRAM (Synchronous Dynamic Random Access Memory)
A variant on the DRAM chip designed to run at the speed of the system clock, thus accelerating the periodic refresh cycle times. SDRAM can run at much higher clock speeds than previous types of DRAM. Basic SDRAM is now obsolete and has been replaced by DDR/ DDR2/3 SDRAM.
A security system offered by UEFI (Unified Extensible Firmware Interface) that is designed to prevent a computer from being hijacked by malware.
A material that can act as both a conductor and an insulator, which provides switch-like functionality, where a circuit can be opened and closed, used to represent binary (on/off) digits.
Asynchronous serial transmission (RS-232) is one of the oldest PC bus standards. A serial port is a legacy port that can be used to connect devices such as modems, mice, and Uninterruptible Power Supplies (UPS). Serial ports transmit data bit-by-bit using a single data line at a speed of up to about 115 Kbps. Although the original serial port used a 25-pin male D connector, most PCs today use a male DB9 (9-pin) port. The serial port is now little used but does provide an "out-of-band" means of configuring network appliances such as switches and routers.
A solution in which one or more virtual servers are created on a physical server in which each virtual server acts like it was a separate computer.
SIM (Subscriber Identity Module)
A small chip card that identifies the user and phone number of a mobile device via an International Mobile Subscriber Identity (ISMI). A SIM card also provides a limited amount of local storage for contacts.
SLAT (Second Level Address Translation)
A feature of virtualization software designed to improve the management of virtual (paged) memory.
SMB (Server Message Block)
A protocol used for requesting files from Windows servers and delivering them to clients. SMB allows machines to share files and printers, thus making them available for other machines to use. SMB client software is available for UNIX-based systems. Samba software allows UNIX and Linux servers or NAS appliances to run SMB services for Windows clients.
SMF (Single Mode Fiber)
A category of fiber optic cable. SMF is more expensive than MMF (using high quality cable and optics) and supports much longer distances (up to about 70 km).
SMP (symmetric multiprocessing)
A condition where two or more physical CPUs that share a common OS and memory execute instructions simultaneously.
SMTP (Simple Mail Transfer Protocol)
The protocol used to send mail between hosts on the Internet. Messages are sent over TCP port 25.
SNMP (Simple Network Management Protocol)
A protocol for monitoring and managing network devices. A management system collates data sent by agents running on each device. The agents maintain a Management Information Base of configuration and usage data. An agent can also generate a trap, alerting the management system of some notable event (such as a printer being out of paper). SNMP works over UDP ports 161 and 162 by default.
SODIMM (Small Outline Dual In-line Memory Module)
Memory that is half the size of DIMMs, are available in 32- or 64-bit data paths, and are commonly found in laptops and iMac systems.
SSH (Secure Shell)
A remote administration and file copy program that is flexible enough to support VPNs too (using port forwarding).
SSH runs on TCP port 22.
SSID (Service Set ID)
Identifies a particular Wireless LAN (WLAN). This "network name" can be used to connect to the correct network. When multiple APs are configured with the same SSID, this is referred to as an E(xtended)SSID.
SSL (Secure Sockets Layer)
A security protocol developed by Netscape to provide privacy and authentication over the Internet. It is application independent (working at layer 5 [Session]) and can be used with a variety of protocols, such as HTTP or FTP. Client and server set up a secure connection through PKI (X.509) certificates (optionally, both client and server can authenticate to one another). The protocol is now being developed as Transport Layer Security (TLS).
SSO (Single Sign-on)
Any authentication technology that allows a user to authenticate once and receive authorizations for multiple services.
Kerberos is a typical example of an authentication technology providing SSO.
SSTP (Secure Socket Tunneling Protocol)
Uses the HTTP over SSL protocol and encapsulates an IP packet with an SSTP header.
(Straight Tip connector)
Bayonet-style twist-and-lock connector for fiber optic cabling.
Used to firmly attach the motherboard to the case, ensuring no other part of the motherboard touches the case.
structured cabling system
The use of patch cords, permanent links, and patch panels.
An IP address consists of a Network ID and a Host ID. The subnet mask is used in IPv4 to distinguish these two components within a single IP address. The typical format for a mask is 255.255.0.0.
CPUs process multiple instructions at the same time (for example, while one instruction is fetched, another is being decoded, another is being executed, and another is being written back to memory).
Superscalar architectures feature longer pipelines with multiple stages but shorter actions (micro-ops) at each stage.
Apple's programming language for developing mobile apps.
Ethernet switches are at the heart of most local networks. A switch receives incoming data into a buffer, then the destination MAC address is compared with an address table. The data is then only sent out to the port with the corresponding MAC address.
In a switched network, each port is in a separate collision domain (microsegmentation). Advanced switches perform routing at layers 3 (IP), 4 (TCP), or 7 (Application). Switches routing at layer 4/7 are referred to as load balancers and content switches.